Dikerogammarus villosus, also known as the killer shrimp,[1][2] is a species of amphipod crustacean native to the Ponto-Caspian region of eastern Europe, but which has become invasive across the western part of the continent.

[2][4] It is thought to have first escaped from the Danube in 1992 when the Rhine–Main–Danube Canal was opened and has since spread to nearly all the major rivers in western Europe, including the Rhône, Loire, Seine, Moselle, Meuse, Rhine and Main, as well as the Baltic Sea.

Its spread is thought to be related to the previous introduction of the zebra mussel, Dreissena polymorpha which it has evolved alongside.

[8] There are fears that it could spread to the Great Lakes in North America in future, carried in the ballast water of ships.

[2] In its natural range, D. villosus is not the most abundant species of amphipod and it does not behave as aggressively as it does in areas it has invaded.

[6] D. villosus can colonise many types of habitat as it is able to tolerate a wide range of temperatures (0–30 °C or 32–86 °F), low oxygen concentrations, and salinity up to 20‰.

[9] It is thought that zebra mussels change habitats by increasing the amount of benthic organic matter, which benefits D. villosus helping them to outcompete other species.